The present invention concerns a device for cutting and/or slitting a travelling web or sheet-like material to form a blank for a box-type package, which device includes a frame supporting two crosswise rotating shafts situated on either side of the path of the travelling web, a pair of rotary circular knives, each provided with a sliding sleeve for positioning the knives on the shaft as a pair of coacting knives, and means for axially pressing the knives together with a desired axial pretension.
The device is generally used in a lengthwise creasing and slitting machine. For an easy understanding of the operation of such a machine, reference is made to FIG. 1 of the attached drawings, wherein a web or sheet B, for instance of corrugated board, is travelling through in a flat plane which extends basically perpendicular to the plane of the Figure. The machine or device is equipped with a pair of circular rotary tools, such as circular rotary knives 1 and 1', which are constructed to cut the web B lengthwise, i.e., in the travelling direction. The knives 1 and 1' cut the web B in a way similar to the action of scissors, which is to say that the cutting is achieved by means of the two peripheral edges 1a and 1'a of the knives 1 and 1', respectively. To this aim, each of the edges 1a and 1'a are bevelled and are axially pressed together under the effect of an elastic pretension by means for axially pressing. Both the knives 1 and 1' are mounted on their own rotary shafts 10 and 10' , respectively, so as to be positioned with the knife 1, as illustrated below the web B, and the knife 1' above the web B. For the crosswise positioning of the lengthwise cutting action, the prior art devices had each knife 1 and 1' mounted on shiftable hollow sleeves 2 and 2', respectively, which allow the setting in the desired axial position. The shifting means consist generally of a suitable fork, which is not illustrated, which engages the sleeves 2 and 2'. As a rule, several slitting tools were provided on the two shafts 10 and 10'. Due to the lengthwise shifting, the sleeves 2 and 2' on the shafts 10 and 10', there is possibility to put the two edges 1a and 1'a of the tool pairs 1 and 1' into contact with or set apart from one another.
To achieve the above-mentioned elastic pretension with the two rotary knives, the prior art specified that one of the two knives be arranged on a ring 3, which itself is fitted with a slight axial clearance with regard to the sleeve. Moreover, several spiral springs were arranged circularly and intercalated between the sleeve and the ring to form the means for elastic pretensioning, with the two knives placed one against the other in the operation position. However, the circular, non-continuous arrangement of the springs around the knife has a drawback of causing a rather erratic, for example jerky, operation of the knife pair when rotating.